Turbine stage cooling

ABSTRACT

A turbine injection system for a gas turbine engine includes a first end operable to receive air from a heat exchanger, a second end operable to distribute mixed cooling air to a turbine stage, an opening downstream of said first end and a mixing plenum downstream of said first end and said opening. The opening provides a direct fluid pathway into said turbine injection system.

TECHNICAL FIELD

The present disclosure relates generally to turbine stage cooling for agas turbine engine, and more specifically to a method and apparatus forcooling a turbine stage using an overcooled cooling fluid supply.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.62/008,805 filed Jun. 6, 2014.

BACKGROUND

Current high performance gas turbine engines utilize various techniquesto maximize performance of the gas turbine engine. One effect of theperformance maximization techniques is an increase in the temperature offluid exiting a high pressure compressor section of the gas turbineengine. The fluid exiting the high pressure compressor section isreferred to as a high pressure compressor discharge and is dischargedinto a combustor section. The increased temperature of the high pressurecompressor discharge may exceed optimum cooling temperatures of coolingair for at least one stage of a high pressure turbine.

Some existing gas turbine engines cool at least the first stage of thehigh pressure turbine by redirecting a portion of the high pressurecompressor discharge onto the first stage of the high pressure turbine.As the discharge air is cool, relative to the temperature of the turbinestage, this provides a cooling effect. When the temperature of the highpressure compressor discharge air exceeds optimum cooling temperaturesof the turbine stage, the cooling capability of the discharge air isreduced, and the workable lifespan of the cooled turbine stage may becorrespondingly reduced.

SUMMARY OF THE INVENTION

An exemplary embodiment of a gas turbine engine includes a compressorsection having a plurality of compressor stages, a combustor disposedwithin a combustor section, wherein the combustor section is fluidlyconnected to the compressor section, a turbine section fluidly connectedto the combustor, the turbine section having at least one stage, acooling air exit disposed on a wall of the combustor section, a firstfluid pathway connecting the cooling air exit to an input of a heatexchanger, a second fluid pathway connecting a first output of the heatexchanger to a turbine injection system, an opening fluidly connectingthe turbine injection system to the combustor section, and a mixingplenum downstream of the opening.

In a further example of the above embodiment, the cooling air exit isdisposed on a radially outward wall of the combustor section.

In a further example of any of the above embodiments, the heat exchangerfurther comprises a second output, and wherein the second output isfluidly connected to at least one other engine component, therebyproviding cooling air to the at least one other engine component.

In a further example of any of the above embodiments the at least oneother engine component includes an engine bearing compartment.

In a further example of any of the above embodiments the mixing plenumis a segment of the turbine injection system downstream of the opening.

In a further example of any of the above embodiments the mixing plenumis disposed between an output of the turbine injection system and theturbine section.

In a further example of any of the above embodiments air entering theturbine injection system from the heat exchanger is below a firstthreshold temperature.

In a further example of any of the above embodiments air entering theturbine injection system through the opening is above a second thresholdtemperature, the second threshold temperature being higher than thefirst threshold temperature.

In a further example of any of the above embodiments air exiting themixing plenum is at a temperature between the first threshold and thesecond threshold.

A further example of any of the above embodiments includes a controllercontrollably coupled to the buffer heat exchanger and operable tocontrol active cooling operations of the heat exchanger.

A further embodiment of any of the above examples includes at least oneof a valve disposed in the cooling air exit and a valve disposed in theopening.

In a further example of any of the above embodiments at least one of thevalve disposed in the cooling air exit and the valve disposed in theopening is controllably coupled to the controller.

An exemplary embodiment of a turbine injection system for a gas turbineengine includes a first end operable to receive air from a heatexchanger, a second end operable to distribute mixed cooling air to aturbine stage, an opening downstream of the first end, wherein theopening provides a direct fluid pathway into the turbine injectionsystem, and a mixing plenum downstream of the first end and the opening.

In a further example of any of the above embodiments air at the firstend is at a temperature below a first threshold temperature.

In a further example of any of the above embodiments a temperature ofair at the opening exceeds a second threshold temperature, and whereinthe second threshold temperature is in greater than the first thresholdtemperature.

In a further example of any of the above embodiments a temperature ofair at a downstream end of the mixing plenum is between the firstthreshold temperature and the second threshold temperature.

An exemplary embodiment of a method for providing cooling air to aturbine stage in a gas turbine engine includes extracting air from acombustor section, cooling the air using a heat exchanger, providing afirst portion of the air to a cooling plenum, mixing the first portionof the air with combustor air in the cooling plenum, thereby achieving adesired cooling air temperature, and providing a second portion of theair to at least one other component of the gas turbine engine directlyfrom the heat exchanger.

In a further example of any of the above embodiments mixing the firstportion of the air with combustor air in the cooling plenum comprisesreceiving air directly from the combustor section through a turbineinjection system opening upstream of the mixing plenum.

In a further example of any of the above embodiments cooling the airusing a heat exchanger comprises overcooling the air below a firstthreshold temperature, wherein the first threshold temperature is aminimum temperature required to provide full cooling of at least oneturbine stage without overcooling the at least one turbine stage.

In a further example of any of the above embodiments mixing the firstportion of the air with combustor air in the cooling plenum, therebyachieving a desired cooling air temperature comprises mixing overcooledair from the heat exchanger with air directly from the combustor section

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a gas turbine engine.

FIG. 2 schematically illustrates a partial view of the gas turbineengine of FIG. 1.

FIG. 3 schematically illustrates a cooling air pipe for use in the gasturbine engine of FIG. 1.

FIG. 4 is a flowchart illustrating a process for partially overcoolingturbine stage cooling air.

DETAILED DESCRIPTION OF AN EMBODIMENT

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. Alternative engines mightinclude an augmentor section (not shown) among other systems orfeatures. The fan section 22 drives air along a bypass flow path B in abypass duct defined within a nacelle 15, while the compressor section 24drives air along a core flow path C for compression and communicationinto the combustor section 26 then expansion through the turbine section28. Although depicted as a two-spool turbofan gas turbine engine in thedisclosed non-limiting embodiment, it should be understood that theconcepts described herein are not limited to use with two-spoolturbofans as the teachings may be applied to other types of turbineengines including three-spool architectures.

The exemplary engine 20 generally includes a low speed spool 30 and ahigh speed spool 32 mounted for rotation about an engine centrallongitudinal axis A relative to an engine static structure 36 viaseveral bearing systems 38. It should be understood that various bearingsystems 38 at various locations may alternatively or additionally beprovided, and the location of bearing systems 38 may be varied asappropriate to the application.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a first (or low) pressure compressor 44 and afirst (or low) pressure turbine 46. The inner shaft 40 is connected tothe fan 42 through a speed change mechanism, which in exemplary gasturbine engine 20 is illustrated as a geared architecture 48 to drivethe fan 42 at a lower speed than the low speed spool 30. The high speedspool 32 includes an outer shaft 50 that interconnects a second (orhigh) pressure compressor 52 and a second (or high) pressure turbine 54.A combustor 56 is arranged in exemplary gas turbine 20 between the highpressure compressor 52 and the high pressure turbine 54. A mid-turbineframe 57 of the engine static structure 36 is arranged generally betweenthe high pressure turbine 54 and the low pressure turbine 46. Themid-turbine frame 57 further supports bearing systems 38 in the turbinesection 28. The inner shaft 40 and the outer shaft 50 are concentric androtate via bearing systems 38 about the engine central longitudinal axisA which is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path C. The turbines 46, 54 rotationally drivethe respective low speed spool 30 and high speed spool 32 in response tothe expansion. It will be appreciated that each of the positions of thefan section 22, compressor section 24, combustor section 26, turbinesection 28, and fan drive gear system 48 may be varied. For example,gear system 48 may be located aft of combustor section 26 or even aft ofturbine section 28, and fan section 22 may be positioned forward or aftof the location of gear system 48.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than about ten (10), thegeared architecture 48 is an epicyclic gear train, such as a planetarygear system or other gear system, with a gear reduction ratio of greaterthan about 2.3 and the low pressure turbine 46 has a pressure ratio thatis greater than about five. In one disclosed embodiment, the engine 20bypass ratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout five (5:1). Low pressure turbine 46 pressure ratio is pressuremeasured prior to inlet of low pressure turbine 46 as related to thepressure at the outlet of the low pressure turbine 46 prior to anexhaust nozzle. The geared architecture 48 may be an epicycle geartrain, such as a planetary gear system or other gear system, with a gearreduction ratio of greater than about 2.3:1. It should be understood,however, that the above parameters are only exemplary of one embodimentof a geared architecture engine and that the present invention isapplicable to other gas turbine engines including direct driveturbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, withthe engine at its best fuel consumption—also known as “bucket cruiseThrust Specific Fuel Consumption (‘TSFC’)”—is the industry standardparameter of lbm of fuel being burned divided by lbf of thrust theengine produces at that minimum point. “Low fan pressure ratio” is thepressure ratio across the fan blade alone, without a Fan Exit Guide Vane(“FEGV”) system. The low fan pressure ratio as disclosed hereinaccording to one non-limiting embodiment is less than about 1.45. “Lowcorrected fan tip speed” is the actual fan tip speed in ft/sec dividedby an industry standard temperature correction of [(Tram ° R)/(518.7°R)]0.5. The “Low corrected fan tip speed” as disclosed herein accordingto one non-limiting embodiment is less than about 1150 ft/second.

FIG. 2 schematically illustrates the combustor section 26 and a portionof the high pressure turbine 54 of FIG. 1, in greater detail. Duringoperation of the gas turbine engine 20, high pressure compressordischarge fluid exits the high pressure compressor section 24 via acompressor section discharge 120. The compressor section discharge 120directs the discharged fluid into a combustion chamber 130 which housesand surrounds the combustor 56. Combustion gasses are expelled from thecombustor 56 into the high pressure turbine 54 due to the ignition offuel within the combustor 56. The expelled combustion gasses are at ahigh temperature and drive the rotors 110, 112 of the turbine section 54to rotate. Due to the extreme temperatures, the combustion gasses alsoheat the high pressure turbine 54 and necessitate cooling.

A cooling air exit 132 is located on a radially outward edge of thecombustor chamber 130 and allows a portion of the discharge fluid fromthe high pressure compressor section 52 to be transferred to a heatexchanger 140. In some examples, the heat exchanger 140 is referred toas an overcooled turbine cooling air (Tcla) heat exchanger (HEX). Thefluid from the compressor section discharge 120 enters the combustorchamber 130, and a portion of the compressor section discharge isremoved from the combustor chamber 130 through the cooling air exit 132.This portion is referred to as the actively cooled air 134. The coolingair exit 132 can be valved in some examples, allowing a controller 190to control an amount of air transferred to the heat exchanger 140. Inother examples, the cooling air exit 132 can include multiple openingsdistributed circumferentially about the outer diameter. In yet furtherexamples, the cooling air exit 132 can be metered allowing a constantvolume of fluid through the cooling air exit 132.

The actively cooled air 134 is directed to the heat exchanger 140. Theheat exchanger 140 cools the actively cooled air 134 using known coolingtechniques. In some examples, the heat exchanger 140 is connected to acontroller 190, and the controller 190 controls the cooling of theactively cooled air 134 based on operating conditions of the turbineengine 20, or any other factor. Once the actively cooled air 134 hasbeen cooled in the heat exchanger 140, the air is output from the heatexchanger 140 through an overcooled turbine airflow 144 and a buffercooling air flow 142. In the illustrated example, the buffer cooling airflow 142 is provided to a bearing compartment 160. In alternate examplesthe buffer cooling air flow 142 can be provided to any other gas turbineengine component for cooling, and is not limited to providing bearingair.

The overcooled turbine cooling airflow 144 passes through a turbineinjector 148 to a mixing plenum 152. Immediately prior to the mixingplenum 152 in the turbine injector 148 is an opening 136 directlyconnecting the turbine injector 148 to the combustor chamber 130. Theopening 136 provides a direct flowpath allowing compressor discharge air150 to enter the turbine injector pipe 148 from the combustor chamber130. The compressor discharge air 150 and the overcooled cooling airflow144 mix in the mixing plenum 152 to form a desired temperature coolingairflow 154. In some examples, the desired temperature of the coolingairflow is a range of temperatures with a first temperature threshold asthe lower bound of the range and a second temperature threshold as theupper bound of the range. In these examples, a fluid having atemperature below the first threshold is overcooled. Similarly, a fluidhaving a temperature above the second threshold is too hot for cooling.The desired temperature cooling airflow 154 is directed onto a turbinefirst stage 110 by the turbine injector 148 and cools the first turbinestage 110. In alternate examples, the desired temperature coolingairflow 154 can also be directed toward the second stage 112 of the highpressure turbine 54 and preform the same cooling aspects.

Furthermore, while illustrated herein as a portion of the turbineinjector 148, the mixing plenum 154 can be a separate chamber fed by theturbine injector 148, with the separate chamber in turn directing thedesired temperature cooling airflow 154 onto the turbine first stage110.

With continued reference to FIG. 2, FIG. 3 schematically illustrates aportion of a turbine injector 200, such as the turbine injector 148illustrated in FIG. 2. The turbine injector 200 includes a body 210having a primary portion 220 that directs an overcooled cooling airflow144 from the heat exchanger 140 to a mixing plenum 214. The illustratedmixing plenum 214 is an end portion of the body 210 immediately after anopening 212. The opening 212 connects the turbine injector 148 to acombustion chamber 130 and receives compressor discharge air 230directly from the combustion chamber 130. The compressor discharge airis too hot to provide full cooling.

The compressor discharge air 230 and the overcooled cooling airflow 144are mixed in the mixing plenum 214 in a mixing flow 240. Once fullymixed, the turbine injector 200 outputs turbine cooling air 250 throughan end opening 252. The end opening 252 is positioned and oriented suchthat turbine cooling air is directed onto the first stage 110 of thehigh pressure turbine 54, thereby cooling the rotor blade and rotordisks of the first stage 110.

FIG. 4 illustrates a flowchart 300 showing a general process forproviding cooling air to the first turbine stage using the apparatus ofFIG. 2. Initially, the discharge air is directed to the heat exchanger140 in a “Direct Discharge Air to Heat Exchanger” step 310. The heatexchanger 140 overcools the actively cooled air using any known heatexchange technique in an “Overcool Actively Cooled Air” step 320. Theovercooled air is then mixed with direct discharge air in a “MixActively Cooled Air with Discharge Air” step 330. The mixed air is thenprovided as cooling air to the first stage of the high pressure turbine54 in a “Supply Cooled Cooling Air to Turbine Stage” step 340.

Referring again to FIGS. 2 and 3, during practical operation of the gasturbine engine 20, the buffer heat exchanger 140 cools the activelycooled air 134 to be within a temperature range required to adequatelycool the bearing compartment 160. The temperature required to adequatelycool the bearing compartment 160 is lower than the optimum temperaturerange required to cool the first turbine stage in the high pressureturbine 54. In a system that provides air directly from the heatexchanger 140 to the first turbine stage 110 as turbine cooling air, theturbine cooling air is cooler than required for properly cooling theturbine first stage. In this situation, the turbine cooling air isreferred to as being overcooled.

While the heat exchanger 140 overcools the overcooled cooling airflow144 that passes through the heat exchanger 140, the amount of overcooledcooling airflow 144 passing through the heat exchanger 140 in theillustrated example is less than the total volume of air required forcooling the corresponding turbine stage.

In order to provide a sufficient volume of the actively cooled air 134,a portion of the compressor section discharge air 150 is combined withthe overcooled cooling airflow 144 in the mixing plenum 152 as describedabove. The addition of the compressor discharge air 150 to theovercooled cooling airflow 144 raises the end temperature of the mixedcooling air 154 and increases the volume of the mixed cooling air 154 todesired levels. The mixing plenum 152 is sized such that mixed coolingair 154 exiting the mixing plenum is fully mixed with an eventemperature and flow characteristic at an exit of the mixing plenum. Asa result, a steady stream of mixed cooling air 154 having a singletemperature is directed onto the corresponding turbine stage.

By tuning the amount of airflow in the overcooled cooling airflow 144output from the heat exchanger 140, the resultant temperature and volumeof the mixed cooling air 154 can be controlled or adjusted in order toachieve a desired volume and temperature for the air cooling thecorresponding turbine stage. In some examples, the amount of overcooledcooling airflow 144 output by the buffer heat exchanger 140 is set at asingle volume during manufacturing of the gas turbine engine 20. Inalternative examples, the volume of airflow in the overcooled coolingairflow 144, and thus the temperature and volume of the mixed air 154,can be reduced or increased by the controller 190 during operation ofthe gas turbine engine in response to engine conditions, atmosphericconditions, or any other conditions. In the controlled example, acontrollable valve structure is installed at the cooling air exit 132,the overcooled airflow 144 exit from the heat exchanger 140, or both.The controllable valve structure is connected to the controller 190allowing the controllable valve structure to adjust a volume of airpassing through the controllable valve structure.

It is further understood that any of the above described concepts can beused alone or in combination with any or all of the other abovedescribed concepts. Although an embodiment of this invention has beendisclosed, a worker of ordinary skill in this art would recognize thatcertain modifications would come within the scope of this invention. Forthat reason, the following claims should be studied to determine thetrue scope and content of this invention.

1. A gas turbine engine comprising: a compressor section having aplurality of compressor stages, a combustor disposed within a combustorsection, wherein the combustor section is fluidly connected to thecompressor section, a turbine section fluidly connected to thecombustor, said turbine section having at least one stage, a cooling airexit disposed on a wall of said combustor section, a first fluid pathwayconnecting said cooling air exit to an input of a heat exchanger, asecond fluid pathway connecting a first output of said heat exchanger toa turbine injection system, an opening fluidly connecting said turbineinjection system to said combustor section, and a mixing plenumdownstream of said opening.
 2. The gas turbine engine of claim 1,wherein the cooling air exit is disposed on a radially outward wall ofthe combustor section.
 3. The gas turbine engine of claim 1, wherein theheat exchanger further comprises a second output, and wherein saidsecond output is fluidly connected to at least one other enginecomponent, thereby providing cooling air to the at least one otherengine component.
 4. The gas turbine engine of claim 3, wherein the atleast one other engine component includes an engine bearing compartment.5. The gas turbine engine of claim 1, wherein said mixing plenum is asegment of said turbine injection system downstream of said opening. 6.The gas turbine engine of claim 1, wherein said mixing plenum isdisposed between an output of said turbine injection system and saidturbine section.
 7. The gas turbine engine of claim 1, wherein airentering said turbine injection system from said heat exchanger is belowa first threshold temperature.
 8. The gas turbine engine of claim 7,wherein air entering said turbine injection system through said openingis above a second threshold temperature, the second thresholdtemperature being higher than the first threshold temperature.
 9. Thegas turbine engine of claim 8, wherein air exiting said mixing plenum isat a temperature between the first threshold and the second threshold.10. The gas turbine engine of claim 1, further comprising a controllercontrollably coupled to said buffer heat exchanger and operable tocontrol active cooling operations of said heat exchanger.
 11. The gasturbine engine of claim 10, further comprising at least one of a valvedisposed in said cooling air exit and a valve disposed in said opening.12. The gas turbine engine of claim 11, wherein at least one of saidvalve disposed in said cooling air exit and said valve disposed in saidopening is controllably coupled to said controller.
 13. A turbineinjection system for a gas turbine engine comprising: a first endoperable to receive air from a heat exchanger, a second end operable todistribute mixed cooling air to a turbine stage, an opening downstreamof said first end, wherein said opening provides a direct fluid pathwayinto said turbine injection system, and a mixing plenum downstream ofsaid first end and said opening.
 14. The turbine injection system ofclaim 13, wherein air at said first end is at a temperature below afirst threshold temperature.
 15. The turbine injection system of claim13, wherein a temperature of air at said opening exceeds a secondthreshold temperature, and wherein the second threshold temperature isin greater than the first threshold temperature.
 16. The turbineinjection system of claim 13, wherein a temperature of air at adownstream end of said mixing plenum is between said first thresholdtemperature and said second threshold temperature.
 17. A method forproviding cooling air to a turbine stage in a gas turbine enginecomprising: extracting air from a combustor section, cooling said airusing a heat exchanger, providing a first portion of said air to acooling plenum, mixing said first portion of said air with combustor airin said cooling plenum, thereby achieving a desired cooling airtemperature, and providing a second portion of said air to at least oneother component of the gas turbine engine directly from said heatexchanger.
 18. The method of claim 17, wherein mixing said first portionof said air with combustor air in said cooling plenum comprisesreceiving air directly from said combustor section through a turbineinjection system opening upstream of said mixing plenum.
 19. The methodof claim 17, wherein cooling said air using a heat exchanger comprisesovercooling said air below a first threshold temperature, wherein thefirst threshold temperature is a minimum temperature required to providefull cooling of at least one turbine stage without overcooling the atleast one turbine stage.
 20. The method of claim 17, wherein mixing saidfirst portion of said air with combustor air in said cooling plenum,thereby achieving a desired cooling air temperature comprises mixingovercooled air from said heat exchanger with air directly from saidcombustor section.